The present invention relates to apparatus for treating a suspension of papermaking stock and more particularly relates to apparatus for cleaning and deaerating a papermaking suspension to provide a papermaking stock supply for a papermaking machine.
In the papermaking art, it long has been known advantageous to deaerate the aqeuous suspension of papermaking fiber prior to its delivery to the papermaking machine. Patents which disclose apparatus for such procedure include, inter alia, U.S. Pat. Nos. 1,853,849; 2,571,219; 2,614,656; 2,685,937; 2,642,950; 2,751,031; 3,131,117; 3,432,036; 3,538,680; and 3,720,315. As such patents teach, it is also commonplace to effect cleaning of the stock to separate it into a dirt-rich fraction, commonly known as a "rejects" fraction and a dirt-poor fraction, known as an "accepts" fraction, such separation being effected in a centrifugal suspended solids separating means commonly referred to as a hydrocyclone. The construction and operation of such cleaning device is described, for example, in U.S. Pat. No. 2,377,524.
Where cleaning of the stock is effected, it also is commonplace to employ plural cleaning stages, that is, a first or primary cleaning stage the accepts from which provides the stock feed to the papermaking machine, a secondary cleaning stage the accepts fraction of which is returned to the primary stage for further cleaning and a tertiary stage in which the accepts are or may be returned to the second stage for further cleaning. Additional stages in the system can be cleaned in like manner.
Each cleaning stage generally comprises a plurality of centrifugal cleaners the number in the primary stage being considerably more than the secondary stage and the secondary stage more than the tertiary stage. In modern papermaking plants, hundreds of cleaners can be used in the cleaning and deaeration operations. The practice heretofore has been to supply stock suspension to the cleaners through a manifold to which each individual cleaner is connected by means of piping, flange connections, etc. Where a large number of cleaners are employed in the cleaning stage, as for example in the primary cleaning stage, the use of individual connections to each of the respective cleaners requires that considerable power be expended to overcome frictional and flow losses occurring in the supply and connection structure associated with the cleaners. Moreover, the initial installation costs of mounting a large number of cleaners in a cleaning stage to a manifold and connecting same to an enclosed receiver to which the accepts fractions are delivered is considerable. Furthermore, during operation, it is possible for a cleaner to become unserviceable, i.e., become worn so that its cleaning efficiency is impaired to the extent that it requires replacement. The manner of mounting cleaners heretofore employed has not made it convenient to quickly and readily remove cleaners and replace same with facility.
Employment in papermaking systems of cleaners having plural inlets thereto and which further are submerged in a stock suspension flow are known, U.S. Pat. Nos. 3,747,306; 3,261,467; 3,415,374; 3,486,618 and 3,959,123 disclosing such arrangements. However, in such systems as disclosed in said patents, the cleaners are arranged with their axes disposed horizontally and the cleaners arrayed in horizontal and/or radial array. Thus the placement of the cleaners does not involve taking advantage of the effect of gravity in connection with rejects discharge and hence higher power consumption attends cleaner operation. Moreover, such cleaner arrangements do not use discharge of either accepts or rejects to a condition of vacuum and again and since such discharges are to a submerged flow, higher power consumption is required than is necessary. Since energy costs are constantly increasing it is desirable that the cleaning operation in a papermaking system be made as efficient as possible.
These problems and undesirable features of centrifugal cleaner mountings are solved or lessened by the present invention as will be apparent from the description which follows.